The bone bots are coming.

A new wave of robotically assisted tools for knee and hip replacements is moving into specialty centers and hospitals around Minnesota, and the number of procedures appears poised to spike in 2017. The surgical robots carry big price tags, but people who use them say the cost is made up in quicker recovery times and more predictable results, especially in complex cases.

Last month a Kimball, Minn., woman made state history when she walked out of a surgical center in St. Cloud less than 12 hours after Dr. Eric Green used a robot-guided system to do the first total-knee replacement surgery in Minnesota. In the Twin Cities, Dr. Robert Hartman last year performed the state's first hip replacement and partial-knee joint replacements using robotically guided tools.

The machines represent a significant opportunity for the medical device industry. By 2018, about one-third of all orthopedic surgeons nationally are expected to use robotic systems, compared to about 18 percent today, stock analysts with RBC Capital Markets projected last spring. Doctors cited a lack of early scientific evidence of superior results and the cost of the systems as two of the biggest obstacles to wider adoption.

Orthopedic surgeons think Smith & Nephew's Minnesota-based robotics division will capture as much as 45 percent of the market for the costly machines, while Michigan-based Stryker will hold on to about half the market, the RBC report says. Stryker, whose Mako system has been on the market for almost a decade, hit a sales record last year by selling 72 of the $1.2 million machines.

Robotic tools, and the GPS-like precision guidance systems that make them possible, are also emerging for spine surgery. Medtronic, which had net sales of $645 million in traditional spinal devices and supplies in the most recent quarter, is ramping up investments in an Israeli-designed robotic system that is being re-engineered with Medtronic devices in mind.

That device, the $900,000 MazorX, is slated for commercial launch at an industry conference in Boston next month, and two competitors are preparing their own robotic spine surgery systems.

"It's providing the tools so they [doctors] can do the precise execution of the best medicine. And there will be different platforms, and I think that's good," said Chris Prentice, CEO of Mazor Robotics Inc., the U.S. branch of the company Medtronic is investing in. "There will be different platforms for specific specialties, and even specific tasks within the specialty."

The original medical robot on the U.S. commercial market is the da Vinci Surgical System, marketed by Silicon Valley's Intuitive Surgical since its approval by the Food and Drug Administration in 2000.

The $1.5 million da Vinci machine operates on soft tissues, like the prostate and uterus. Its robotic arms reach inside the body and mimic movements that a surgeon makes on external controls. Intuitive says the device's safety is supported by more than 8,500 peer-reviewed articles, but hundreds of plaintiffs have sued over alleged injuries from the machine, raising questions about physician training programs.

Meanwhile, American corporate heavyweights Johnson & Johnson and Google have jointly funded a company called Verb Surgical, whose lofty aims, according to its website, include creating "a future unimagined even a few years ago, which will involve machine learning, robotic surgery, instrumentation, advanced visualization, and data analytics."

Robotics systems for surgery on the skeleton, in contrast, are targeting quick growth in the present. And they may get a significant boost from Medicare.

Last month the outpatient advisory panel for the federal Center for Medicare and Medicaid Services recommended that the government insurer for people age 65 and older start covering total-knee replacement surgery in same-day surgery centers, instead of just covering the procedure with overnight hospital stays.

Until recently, orthopedic robotic surgical systems were FDA approved only for partial-knee replacements, which involve precise removal of potato-chip sized slices of bone on one side of the knee and replacing them with metal and plastic implants. But the large majority of knee-replacement surgeries are for "total knee" procedures, which slice off the top of the shin bone and heavily reshape the bottom of the knee bone.

Several robotic systems now have FDA clearance for total-knee replacements, including Stryker's Mako system and Smith & Nephew's Navio system. Both Medicare and the device companies have noted that demand for total-knee surgery is expected to climb sharply as baby boomers move into their active retirement years.

Stryker's Mako system is the longest-running orthopedic robot. The company says its system for hip and knee replacement surgery (it got total-knee clearance last year) is poised to take off in 2017 after a relatively long road to acceptance by the public and regulators.

Although 2016 marks 10 years of clinical use of the Mako system, there are only about 300 of the $1.2 million machines in the nation. Minnesota's first Mako unit was purchased last year by the Minnesota Valley Surgery Center in Burnsville. Soon after, two more units were acquired by health care providers in St. Cloud.

"Investing in a robotics program is a big decision for a hospital and for a doctor," said Stuart Simpson, general manager of Stryker's commercial business unit that includes robotics. "Doctors and hospitals, quite rightly, don't make these decisions on a whim. So there's been a lot of conversation, a lot of interest."

Active sales talks are ongoing with health care providers in Minnesota, Simpson said. The machine has a robotic arm that the physician grasps and directs to the hip or knee joint being replaced. It uses precision navigation similar to GPS to stop the arm from moving beyond the intended cutting area.

The newest entry to the market is the Navio, designed by Plymouth-based Blue Belt Technologies and acquired by Smith & Nephew late last year. Three of the $495,000 systems are in use in Minnesota, including one at Twin Cities Orthopedics in Coon Rapids and the unit at the St. Cloud Surgical Center where Kimball resident Vicki Woods got the state's first robotic total-knee replacement last month, on her 54th birthday.

"It was same-day surgery. I walked out about 4:15 that afternoon," Woods said, adding that she used a walker when she left the hospital but needed it for only three days. "Not everybody gets a new knee for their birthday."

There are 75 Navios in use in the U.S. Rather than robotic arms, the Navio's surgical instrument is contained in a hand-held cutting tool that is tracked with precision guidance. The system automatically pauses the motion of the cutting tool if the surgeon moves it beyond the intended area.

Both the Navio and Mako use detailed 3-D modeling of patients' actual anatomy to not only track the motion of the surgical tools, but to model the biomechanics of the implant beforehand, theoretically ensuring the best alignment and extending the life of the implant. The systems are designed to allow for the least-invasive surgery available.

Surgeons Green and Hartman said their patients appear to prove the promise of lower complication rates and reliable alignment. But since such joints are supposed to last 15 years or more, it's not yet possible to statistically compare the longest-term outcomes of robotic vs. traditional techniques.

"The biggest thing that mattered to me were the words, 'You will heal quicker and better,' " Woods said. "Otherwise, sure, I am for new technology."

Joe Carlson • 612-673-4779